/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.heron.api.windowing;

import java.io.Serializable;

/**
 * An event is a wrapper object that gets stored in the window.
 *
 * @param <T> the type of the object thats wrapped. E.g Tuple
 */
public interface Event<T extends Serializable> extends Serializable {
  /**
   * The event timestamp in millis. This could be the time
   * when the source generated the tuple or the time
   * when the tuple was received by a bolt.
   *
   * @return the event timestamp in milliseconds.
   */
  long getTimestamp();

  /**
   * Returns the wrapped object, E.g. a tuple
   *
   * @return the wrapped object.
   */
  T get();

  /**
   * If this is a watermark event or not. Watermark events are used
   * for tracking time while processing event based ts.
   *
   * @return true if this is a watermark event
   */
  boolean isWatermark();
}
